@nieuport28 "Considering all the advances being made in Battery Technology. Has there been any discussions on using a battery that could go, say, 60-90 days?"
There already seems to be a reasonable level of adoption of 90 day batteries in ULBs - see:
RJE International - Aviation - Underwater Locator Beacons
Also it seems that there are new regulations (tso-c121b and ED112A ULB) that seem to imply that 90 day battery life for ULBs will be the norm after March 2015 with older 30 day batteries going out of use after that date. I don't know if the rules will require all batteries to be replaced by 90 day ones or if only new installations will require them, but it does seem that the use of 30 day batteries will become a thing of the past.
There seems to be a long European regulatory amendment document at
http://www.easa.europa.eu/system/fil...PA-2013-26.pdf which seems to imply on page 10 that "Mandate that the ULDs of all crash-protected flight recorders have a transmission time of 90 days by 1 January 2020"